A great number of physiological processes involve biologically active peptides, through their interactions with receptors and enzymes. However, peptides are not to be considered ideal drugs, given their poor metabolic stability, rapid excretion and low selectivity for specific receptors. A valid alternative involves the design of peptide analogues which are capable of mimicking the action of the natural peptide at the receptor level (peptidomimetic) [(a) Kahn, M. (Editor). Peptide Secondary Structure Mimetics. Tetrahedron Symposia-in-Print No. 50 1993, 49, 3433-3689. (b) Gante, J. Angew. Chem., Int. Ed. Engl. 1994, 33, 1699-1720. (c) Olson, G. L.; Bolin, D. R.; Bonner, M. P.; Bös, M.; Cook, C. M.; Fry, D. C.; Graves, B. J.; Hatada, M.; Hill, D. E.; Kahn, M.; Madison, V. S.; Rusiecki, V. K.; Sarabu, R.; Sepinwall, J.; Vincent, G. P.; Voss, M. E. J. Med. Chem. 1993, 36, 3039-3049. (d) Kitagawa, O.; Velde, D. V.; Dutta, D.; Morton, M.; Takusagawa, F.; Aubè, J. J. Am. Chem. Soc. 1995, 117, 5169-5178. (e) Giannis, A.; Kolter, T. Angew. Chem.; Int. Ed. Engl. 1993, 32, 1244. (f) Aube, J. Tetrahedron Symposia-in-Print No. 50, 2000, 56, 9725-9842].
During our research into peptide secondary structure mimetics, certain 6,5- and 7,5-azabicycloalkane aminoacids have been synthesised [(a) Colombo, L.; Di Giacomo, M.; Scolastico, C.; Manzoni, L.; Belvisi, L.; Molteni, V. Tetrahedron Lett. 1995, 36, 625; (b) Colombo, L.; Di Giacomo, M.; Belvisi, L.; Manzoni, L.; Scolastico, C. Gazz. Chim. It. 1996, 126, 543; (c) Colombo, L.; Di Giacomo, M.; Brusotti, G.; Sardone, N.; Angiolini, M.; Belvisi, L.; Maffioli, S.; Manzoni, L.; Scolastico, C. Tetrahedron 1998, 54, 5325-5336; (d) Angiolini, M.; Araneo, S.; Belvisi, L.; Cesarotti, E.; Checchia, A.; Crippa, L.; Manzoni, L.; Scolastico, C. Eur. J. Org. Chem. 2000, 2571-2581; (e) Manzoni, L.; Colombo, M.; May, E.; Scolastico, C. Tetrahedron 2001, 57, 249; (f) Belvisi, L.; Colombo, L.; Colombo, M.; Di Giacomo, M.; Manzoni, L.; Vodopivec, B.; Scolastico, C. Tetrahedron 2001, 57, 6463; (g) EF 1 077 218; (h) Colombo, L.; Di Giacomo, M.; Vinci, V.; Colombo, M.; Manzoni, L.; Scolastico, C. Tetrahedron, 2003, 59, 4501-4513; (i) Manzoni, L.; Colombo, M.; Scolastico, C. Tetrahedron Lett. 2004, 45, 2623-2625; (l) Belvisi, L.; Colombo, L.; Manzoni, L.; Potenza, D.; Scolastico, C. Synlett, 2004, 1449-1471.
These structures may be considered as conformationally constrained analogues of the Ala-Pro and Phe-Pro dipeptide units. [(a) Belvisi, L.; Bernardi, A.; Manzoni, L.; Potenza, D.; Scolastico, C. Eur. J. Org. Chem. 2000, 2563-2569; (b) Gennari, C.; Mielgo, A.; Potenza, D.; Scolastico, C.; Piarulli, U.; Manzoni, L. Eur. J. Org. Chem. 1999, 379].
The functionalisation of such molecules with heteroalkyl substituents is an aim of great interest, since the side chains may increase the affinity of the peptide for the receptor by interacting with the hydrophobic or hydrophilic sites of the receptor itself. A further advantage of such systems is the possibility of binding to different pharmacophoric groups and hence the possibility of creating a library, with the member components of which having different biological properties and activities. During our research into peptide secondary structure mimetics, certain 6,5- and 7,5-azabicycloalkane aminoacids have been synthesised which have been functionalised with heteroalkyl appendages [(a) Artale, E., Banfi, G.; Belvisi, L.; Colombo, L.; Colombo, M.; Manzoni, L.; Scolastico, C. Tetrahedron, 2003, 59, 6241-6250; (b) Bracci, A.; Manzoni, L.; Scolastico, C. Synthesis 2003, 2363-2367; (c) Bravin, F. M.; Busnelli, G.; Colombo, M.; Gatti, F.; Manzoni, L.; Scolastico, C. Synthesis, 2004, 353; (d) Manzoni, L.; Belvisi, L.; Colombo, M.; Di Carlo, E.; Formi, A.; Scolastico, C. Tetrahedron Lett. 2004, 45, 6311-6315].
Furthermore, analogously to what occurs for non-substituted conformationally constrained dipeptide mimetics [Belvisi, L.; Bernardi, A.; Checchia, A.; Manzoni, L.; Potenza, D.; Scolastico, C.; Castorina, M.; Cupelli, A.; Giannini, G.; Carminati, P.; Pisano, C. Org. Lett. 2001, 3, 1001, C. Scolastico, L. Manzoni, G. Giannini. Brit. UK Pat. Appl. 2004. GB 2395480] such heteroalkyl substituted lactams may be incorporated into cyclic pseudo-peptides containing RGD sequence.
Such molecules may be selectively targeted to those tissues over-expressing certain receptors (e.g. epithelial cells involved in vascular growth), so as to be able to be used to inhibit angiogenesis and selectively control the release of any drugs optionally bound to the substituent groups on the lactam ring [Arap, W.; Pasqualini, R.; Ruoslahti, E. Science, 1998, 279, 377]. Thus, from a first point of view, the low number of “scaffolds” reported in the literature necessitates the design and synthesis of novel conformationally constrained dipeptide mimetics, functionalised with hetero-substituted side chains for interaction with various receptors.
Moreover, and from another relevant point of view, today is well known that the cell adhesion molecule αvβ3 is an important player in the process of tumor angiogenesis and metastasis. With the term angiogenesis is identified a formation process of new blood vessels that occurs not only during embryonic development and normal tissue growth and repair, but is also associated with the female reproductive cycle, establishment and maintenance of pregnancy, and repair of wounds and fractures. In addition to angiogenesis that occurs in the normal individual, angiogenic events are involved in a number of pathological processes, notably tumor growth and metastasis, and other conditions in which blood vessel proliferation is increased, such as diabetic retinopathy, psoriasis and arthropathies. Angiogenesis is so important in the transition of a tumor from hyperplastic to neoplastic growth, that inhibition of angiogenesis has become an active cancer therapy research field. Tumor angiogenesis differs significantly from physiological angiogenesis. The differences include aberrant vascular structure, altered endothelial cell-pericyte interactions, abnormal blood flow, increased permeability and delayed maturation. Molecules regulating angiogenesis include growth factor receptors, tyrosine kinase receptors, G protein-coupled receptors for angiogenesis modulating proteins, and integrins [Bergers G., L. E. Benjamin, Nat. Rev. Cancer, 2003, 3:401-410; Ferrara N., Nat. Rev. Cancer, 2002, 2:795-803, Nyberg, P., L. Xie, R. Kalluri, Cancer Res., 2005, 65:3967-3979]. Increasing amounts of evidences now imply that integrin signaling plays a key role in tumor angiogenesis and metastasis [Brooks, P. C., R. A. Clark, D. A. Cheresh, 1994, Science, 264:569-571, Kumar, C. C., 2003, Curr. Drug Targets, 4:123-131]. The αvβ3 integrin, in particular, is significantly up-regulated on endothelium during angiogenesis but not on quiescent endothelium [Hood, J. D. and D. A. Cheresh, 2002, Nat. Rev. Cancer, 2:91-1000, Xiong, J. P., T. Stehle, R. Zhang, A. Joachimiak, et al., 2002, Science, 296:151-155, Jin, H. and J. Varner, 2004, Br. J. Cancer, 90:561-565]. Research has shown that tumor expression of integrin αvβ3 correlates well with tumor in several malignancy such as melanoma, glioma, ovarian cancer, and breast cancer. Thus, the ability to quantitatively image integrin αvβ3 expression in vivo in a non-invasive manner may shed new light into the mechanism of angiogenesis and antiangiogenic treatment efficacy based on integrin antagonism. Tumor integrin expression imaging will also aid in lesion detection, to more appropriately select patient for anti-integrin treatment, in new anti-integrin drug development/validation, as well as in treatment monitoring and optimization.
Kessler and coworkers have provided new cyclic RGD based pentapeptides including the optimized c(RGDfV) system [see, for instance, US2002/0198142 and EP 0632053, U.S. Pat. No. 6,001,961] wherein the said pentapeptides are proposed for use, as such, as integrin-inhibitor drugs in the control of diseases, in particular disorders of the circulation, thrombosis, cardiac infarction, arteriosclerosis, inflammations, and angiogenesis. Cited references, however, do not suggest the use of claimed peptides or of suitable derivatives thereof for the diagnostic imaging or radiotherapy of angiogenesis and angiogenic disorders.
EP1068244 discloses pharmaceuticals useful for the diagnosis and treatment of cancer comprising peptides or peptidomimetics targeted to receptors up-regulated during angiogenesis and chelators.
Diagnostic or therapeutic agents including the RGD sequence and, particularly, the above c(RGDfV) cyclic peptides targeted to integrin receptors are also known: [Janssen, M. L., W. J. Oyen, I. Dijkgraaf, et al. 2002, Cancer Res. 62:6146-6151; Haubner, R. H., H. J. Wester, et al. Cancer Res. 61:1781-1785; Haubner, R. H., H. J. Wester, et al. 2003, Q. J. Nucl. Med. 47:189-199; Haubner, R. H., H. J. Wester, 2004, Curr. Pharm. Des. 10:1439-1455; Wang, W., S. Ke, et al. 2004, Mol. Imaging 3:343-351; Sunkuku, K., K. Shi, et al., 2005, Mol. Imaging, 4:75-87, Sipkins D. A., D. A. Cheresh, et al., Nat. Med. 4:623-626].
The said prior art agents, however, generally suffer of drawbacks deriving from poor diffusion or transport, limited availability, and/or lack of specificity all resulting in a modest tumor-to-background ratio, and very low contrast observed in angiogenic regions.
Thus still remains a need for diagnostic and therapeutic agents that, when administered in vivo to a mammal, may combine high specificity and acceptable pharmacokinetic properties.